Cardiovascular diseases [CVD] are the primary causes of morbidity and mortality in the elderly with approximately 80% of the CVD in this age group arising from complications due to atherosclerosis. A common procedure for treating the effects of atherosclerosis is vascular bypass grafting. Unfortunately, the success of the bypass grafts decreases significantly over time. The chief cause of chronic graft failure has been found to be intimal hyperplasia with the primary site of occurrence being the distal anastomosis. The objective of this study is to determine the relationship between biomechanical factors and the development of intimal hyperplasia in the host artery at the distal anastomosis of vascular bypass grafts. It is the purpose of this study to determine the effect of varying the graft- to-artery diameter ratio, DR, upon the development of arterial intimal hyparplasia at the distal anastomosis in chronic animal models. Tapered e-PTFE vascular grafts will be implanted in the carotid arteries of 25 adult, male mongrel dogs weighing between 25 and 30 kg with a distal anastomosis consisting of a DR of either 1.0 or 1.5. Detailed shear rate measurements along the near and far walls of the anastomoses will be made at the time of surgery with a custom made, 20 MHz triple crystal, pulsed Doppler ultrasonic transducer. After 4 months implantation, this data will be compared to histologic measurements at corresponding spatial sites using linear regression analysis to determine any correlation between initial local shear effects and the subsequent development of intimal hyperplasia. Therefore, the null hypothesis of this study is that "the degree of chronic arterial intimal hyperplasia within the distal anastomosis of bypass is not affected by a change in the graft-to-artery diameter ratio".